Re: kvm guest debug using gdb on x86

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Aneesh Kumar K.V wrote:
> On Wed, May 20, 2009 at 10:10:59AM +0200, Jan Kiszka wrote:
>> Aneesh Kumar K.V wrote:
>>> On Wed, May 20, 2009 at 12:23:12AM +0530, Aneesh Kumar K.V wrote:
>>>> Hi,
>>>>
>>>> With the latest qemu-kvm and 2.6.30-rc6 kernel i am not able to get
>>>> the guest debugging with gdb. I get the following error.
>>>>
>>>> $gdb ./vmlinux
>>>> GNU gdb 6.8-debian
>>>> Copyright (C) 2008 Free Software Foundation, Inc.
>>>> License GPLv3+: GNU GPL version 3 or later
>>>> <http://gnu.org/licenses/gpl.html>
>>>> This is free software: you are free to change and redistribute it.
>>>> There is NO WARRANTY, to the extent permitted by law.  Type "show
>>>> copying"
>>>> and "show warranty" for details.
>>>> This GDB was configured as "i486-linux-gnu"...
>>>> (gdb) b do_fork
>>>> Breakpoint 1 at 0xc106cfc8: file kernel/fork.c, line 1347.
>>>> (gdb) target remote localhost:1234
>>>> Remote debugging using localhost:1234
>>>> [New Thread 1]
>>>> Remote 'g' packet reply is too long:
>>>> 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
00
>> 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000
>>>> (gdb)
>>>>
>>>> any patches that i can try ?
>>> Works better with the four patches found at
>>>
>>> http://git.kiszka.org/?p=kvm-userspace.git;a=shortlog;h=refs/heads/queues/gdb
>>>
>>> But a next and continue doesn't get the prompt back on gdb. The guest
>>> does stops the execution.
>> What arch is host and guest (x86-32 or -64)? What KVM versions are you
>> using? Are you sure that guest and vmlinux matches?
>>
> 
> Both host and guest are x86-32.  For kvm user space I did a git clone
> from git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git. I tested with
> commit 22d239bcee126742df46938ee8ddc7c6b9209e23. That version fails
> with the "remote g packet reply is too long" error. Then i applied the
> four patches from your git repo. That gets the guest to stop execution
> on breakpoint, i can check the stack. but single stepping doesn't work.
> 
> Guest kernel I tried was linux-2.6-tip

Does debugging work with -no-kvm, ie. in TCG mode?

Jan

PS: For qemu-kvm.git you can now use my qemu gdb queue directly, ie. you
don't need to rebase manually.

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux
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